In the drilling of wells, a drilling fluid (called mud) is circulated downwardly through the drill strings, flows out through the drill bit, and returns to the surface in the annular space around the drill string within the drilled hole. The drilling fluid is delivered under substantial pressure at large flow rates by a mud pump into the drill stem, circulates along the path just described, and is reclaimed at the surface where it emerges from the annular space around the drill string. The mud is then returned to mud pits or tanks for storage for subsequent recycling. Drilling fluid is expensive to make. Even though a major portion of it is normally water, the drilling fluid costs in drilling in a deep well are not trivial. Rather, the cost can be substantial and to this end, it is desirable to recirculate the drilling fluid. One purpose of the drilling fluid is to remove cuttings from the vicinity of the drill bit as it penetrates various formations of the earth. These cuttings are flushed away from that area by the large volume of drilling fluid. The drilling fluid carries the cuttings back to the surface of the well. Ultimately, the cuttings must be removed even though the drilling fluid is circulated back into the well. Various and sundry devices have been provided heretofore for use in clearing the drilling fluid. As a generalization, these devices have been called "desanders" or "shale shakers". They typically use screens to filter the flow, or alternately some type of sedimentation approach to remove cuttings.
The present disclosure is directed to a device for removing the cuttings from the mud flow. The mud flow is thus returned to the surface and is directed through a mud flow line to the apparatus of the present disclosure. The mud at this point in time must be presumed to include cuttings of all sizes and shapes. That is, some can be as small as sand particles and other pieces can be larger. While this is a matter of scale, it is typical that the cuttings fall into a specific size range which is dependent on the drilling speed, the type of drill bit being used, the weight of the drill stem on the bit, and the type of formation being drilled. Moreover, the mud flow may be gas cut, meaning natural gas from a pentroleum bearing formation has been entrained in the mud flow, and that tends to reduce the weight of the mud and alters its capacity for carrying drill bit cuttings.
This apparatus is a system for removing particulate material from the drilling fluid. The mud that is returned to the surface is delivered to the area where this equipment is operated. In an ordinary situation, it is desirable to use duplicate sets of this equipment so that one is always available for sevice. While one is in service, the other can be shut down momentarily or is taken out of service so that the sceeens in it can be changed from one size to another, or other maintenance be implemented, for example, inspection of the cuttings, etc. Whatever the reason, duplicate sets of equipment are normally preferred so that each of the two sets of equipment can handle the maximum mud flow anticipated in a specific drilling situation.
The present apparatus is a screened rotation system which utilizes a combination of circular screen and rotational speed to catch a selected set of particulates, remove them from the mud stream, and additionally throw them to the side so that the particulate material removed from the mud flow is separated and can be delivered by a suitable conveyer system away from the mud. The mud is filtered through two or three screens which can have the same screen size or which alternately can have different sizes. It is desirable to classify the particles by screen size, and when that is done, the screens progressively have smaller openings. Thus, the mud flow will pass through a first screen which has relatively large openings, a second with intermediate openings, and the mesh in the third screen will be much smaller.
Multiple screen passes have sometimes been difficult to implement. The present apparatus however enables mud cleaning with a series of screens which are stacked one over the other and which are supported on a common central stem having a central drive shaft. The particles are caught on circular screens. The screens are rotated and periodically vibrated to cause particles on the respective screens to bounce or dance. As a result of the rotation, the particles migrate outwardly on the screens and ultimately fall off the outer periphery of the respective screens and are collected downwardly into a funnel shaped housing for removal wherein the housing dumps the cuttings onto a conveyer system. Moreover, this system, while rather compact, can handle a fairly high volume of drilling fluid. It continuously rotates the screens so that blinding of the screens as a result of excessive particulate accumulation on the screen is negligible. The constant rotation coupled with periodic vibration helps clear the particulate accumulation to reduce screen blinding.